1. Field of the Invention
The present invention relates to a glass antenna device for use with an automobile telephone set, and more particularly to a glass antenna device for use as a UHF-band transmission and reception antenna on an automobile window glass panel.
2. Description of the Prior Art
Japanese utility model application No. 4-38628 discloses a glass antenna device for use with an automobile telephone set. As shown in FIG. 24 of the accompanying drawings, the disclosed glass antenna device comprises a radiation pattern P1 having a vertical length of about 1/4 of the wavelength of signals to be radiated, and a ground pattern P2 having a vertical length of about 1/4 of the wavelength of signals to be radiated and a horizontal length ranging from about 1/4 to 3/4 of the wavelength of signals to be radiated. The radiation and ground patterns P1, P2 are adapted to be mounted on a window glass panel of an automobile. The ground pattern P2 has a centrally open shape comprising an outer frame pattern P2a and a central vertical pattern P2b.
The horizontal length of the ground pattern P2 is relatively large, and the radiation pattern P1, particularly its feeder, is located in alignment with the center of the ground pattern P2 in the horizontal direction. Therefore, the glass antenna device cannot be positioned closely to an edge of the window glass panel, i.e., the feeder of the radiation pattern P1 cannot be positioned on a black ceramic strip on the edge of the window glass panel.
Furthermore, since the ground pattern P2 is not connected to an automobile body as ground, telephone communications made through the automobile telephone set are susceptible to various noises produced by other electronic devices, including an FM receiver, TV receiver, etc., which may be mounted on the automobile.
The introduction of noises may be reduced by connecting the ground pattern P2 to the automobile body. However, as the ground pattern P2 has no connection terminals, it is difficult to join a ground line to the ground pattern P2. Even if it is possible to connect the ground pattern P2 to the automobile body, the antenna characteristics of the glass antenna device are altered by the grounding, making it impossible for the glass antenna device to achieve its desired performance.
A known double-loop glass antenna device for automobile telephone is disclosed in Japanese laid-open patent publication No. 4-14304.
As shown in FIG. 25 of the accompanying drawings, the disclosed double-loop glass antenna device, generally designated by the reference numeral 101, has two half-loop conductors 103a, 103b, two reactive conductors 104a, 104b connected to the respective half-loop conductors 103a, 103b, and a ground conductor 105 connected to the reactive conductors 104a, 104b, the conductors 103a, 103b, 104a, 104b, 105 being mounted on a rear or front window glass panel 102. The reactive conductors 104a, 104b are of an L-shaped pattern connected between the half-loop conductors 103a, 103b and the ground conductor 105.
The half-loop conductors 103a, 103b are joined to each other at a feeding point 106 that is connected to a core 107a of a feeder cable 107. The feeder cable 107 includes an outer conductor 107b connected to the ground conductor 105 for feeding the glass antenna device 101 in an unbalanced fashion.
The half-loop conductors 103a, 103b and the ground conductor 105 are horizontally relatively long, and the feeding point 106 is positioned in alignment with the center of the half-loop conductors 103a, 103b and the ground conductor 105 in the horizontal direction. Therefore, the glass antenna device 101 cannot be positioned closely to an edge of the window glass panel 102, i.e., the feeding point 106 cannot be positioned on a black ceramic strip on the edge of the window glass panel 102. Inasmuch as the ground conductor 105 is not connected to an automobile body as ground, telephone communications made through an automobile telephone set connected to the glass antenna device 101 are susceptible to various noises produced by other electronic devices, including an FM receiver, TV receiver, etc., which may be mounted on the automobile.